Nowadays, a variety of commercially-available electronic devices are developed toward small size and light weightiness in order to have the portability. In addition, the electronic devices have touch screens. By inputting commands into the touch screens, the electronic devices can be operated accordingly. For example, the electronic devices include mobile phones, tablet computers, personal digital assistants (PDAs), handheld game consoles (e.g. PSP, NDSL and Gameboy series game consoles), or the like.
Due to the portability of the above electronic devices, these electronic devices cannot be connected with a power source at any time. For providing sufficient electric power to the electronic device, a built-in battery is usually installed in the electronic device. The battery is a chargeable battery. Once a power socket for a power source is available, the electronic device may be plugged into the power socket, so that the chargeable battery of the electronic device is charged by the power source.
In case that the residual battery capacity of the electronic device is insufficient, the chargeable battery of the portable electronic device may be charged through a connecting wire. A first end of the connecting wire is plugged into the electronic device, and a second end of the connecting wire is plugged into a power source or a mobile bank that can store electric power. Under this circumstance, the electric power provided by the power source or the mobile bank may be transmitted to the electronic device through the connecting wire in order to charge the electronic device.
However, the applications of the charging process are usually restricted by the length of the connecting wire. For example, during the process of charging the electronic device, the connecting wire usually becomes hindrance from operating the device or arbitrarily moving the electronic device.
With development of a wireless charging technology, a wireless power transmission device for wirelessly charging the electronic device has been disclosed in order to solve the drawbacks of the wired charging technology of using the connecting wire. FIG. 1 schematically illustrates the relationship between a conventional wireless power transmission device and a conventional portable electronic device. As shown in FIG. 1, the conventional wireless power transmission device 1 comprises a main body 10, a power cable 11, a driving module 12, and a transmitter coil 13. In addition, the conventional portable electronic device 2 comprises a casing 20, a receiver coil 21, and a chargeable battery (not shown).
The power cable 11 of the conventional wireless power transmission device 1 is exposed outside the main body 10 to be connected with a power source (not shown). The driving module 12 and the transmitter coil 13 are both disposed within the main body 10. In addition, the driving module 12 is connected with the power cable 11 and the transmitter coil 13. When the driving module 12 is driven by the power source, the driving module 12 generates an electric current. When the electric current flows through the transmitter coil 13, an electromagnetic effect occurs. In response to the magnetic flux generated by the electromagnetic effect, the transmitter coil 13 outputs a corresponding electric power. The transmitter coil 13 is wound to have a circular shape. On the other hand, the receiver coil 21 is disposed within the casing 20 of the conventional portable electronic device 2 for receiving the electric power from the transmitter coil 13. The chargeable battery is connected with the receiver coil 21. After the electric power is received by the closed receiver coil 21, the electric power is stored in the chargeable battery so as to be utilized.
Generally, the main body 10 of the conventional wireless power transmission device 1 is designed to have a platform profile. In addition, the volume of the main body 10 of the conventional wireless power transmission device 1 is larger than the casing 20 of the conventional portable electronic device 2 in order to facilitate the user to place the conventional portable electronic device 2 thereon. During the process of transmitting the electric power from the conventional wireless power transmission device 1 to the conventional portable electronic device 2, the receiver coil 21 within the conventional portable electronic device 2 should be purposely placed at a position near the transmitter coil 13 of the conventional wireless power transmission device 1. That is, for allowing the receiver coil 21 to receive the electric power, the transmitter coil 13 should be aligned with the closed receiver coil 21 as precisely as possible.
As the size of the electronic device 2 is increased (for example the size of a display screen of the electronic device 2 is increased), the main body 10 of the conventional wireless power transmission device 1 should be correspondingly increased. Consequently, the transmitter coil 13 within the main body 10 is also increased. The transmitter coil 13 is also wound to have a circular shape. As the circularly wound transmitter coil 13 is increased, the distance between the center of the transmitter coil 13 and the circumference of the transmitter coil 13 is increased. Under this circumstance, the magnetic flux generated at the center of the transmitter coil 13 is reduced, and thus the charging efficiency is reduced.
Therefore, there is a need of providing a wireless power transmission device with enhanced charging efficiency.